NM is pretty much tank-and-spank most of the time atm. Dungeon boss may not be higher level or hit harder, but they are trickier. You have to face add, you have to be watch the clock (NM has 30 mins limit, but in order to reach dungeon boss it may or may not take more than 30 mins out of 1 hour. R25-28 Party getting to Shaula the correct way without cheating through return may very much take 40-45 mins and that leaves you 15 mins left for the fight), in R45 Dungeon you have to watch the ghost, eye, shield/sword/eye terminal.